The brains of children with dyslexia may be structured differently, according to neuroimaging of the thalamus, the part of the brain that serves as its connector.

The behavioral characteristics of dyslexia—a reading disorder that affects up to 17 percent of the population—are well documented, including struggling to recognize and decode words as well as trouble with comprehension and reading aloud.

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While many dyslexia studies focus on the cerebral cortex, the new research, published in the journals Brain Connectivity and Brain Research, targeted the sub-cortical thalamus region.

The thalamus serves as the brain’s connector—relaying sensory and motor signals back to the cerebral cortex via nerve fibers that are part of the brain’s “white matter.” The thalamus also regulates alertness, consciousness, and sleep.

Evaluating 40 children ages 8 to 17 years, evenly divided between typically developing readers and those with developmental dyslexia, the researchers used diffusion tensor imaging to visually map the structure of the brain in an effort to better understand the role of the thalamus in reading behavior.

“A different pattern of thalamic connectivity was found in the dyslexic group in the sensorimotor and lateral prefrontal cortices,” says Laurie Cutting, professor of special education and professor of psychology and human development, radiology, and pediatrics at Vanderbilt University.

“These results suggest that the thalamus may play a key role in reading behavior by mediating the functions of task-specific cortical regions. Such findings lay the foundation for future studies to investigate further neurobiological anomalies in the development of thalamo-cortical connectivity in individuals with dyslexia.”

Different connections

In a related study, researchers examined connectivity patterns in a cortical region known to be especially important for reading: the left occipito-temporal region, sometimes referred to as the visual word form area.

While there have been many functional MRI studies examining this region, there is not a consensus on the region’s functionalities, and studies of the visual word form area’s structural connectivity are relatively new.

Cutting and her colleagues used diffusion MRI to study the structural connectivity patterns in the left occipito-temporal region and surrounding areas of the brain in 55 children.

“Findings suggest that the architecture of the left occipito-temporal region connectivity is fundamentally different between children who are typically developing readers and those with dyslexia,” Cutting says.

The typically developing readers showed greater connectivity to linguistic regions than the dyslexic group. Those with dyslexia showed greater connectivity to visual and parahippocampal (memory encoding and retrieval) regions.

The data were collected at Johns Hopkins University School of Medicine’s Kennedy Krieger Institute and the Vanderbilt University Institute of Imaging Science at Vanderbilt University Medical Center. The work was conducted in part using the resources of the Advanced Computing Center for Research and Education at Vanderbilt University.